The present invention concerns a system for driving a pair of double toggle mechanisms arranged extending along the front and backside of each of upper and lower platens in a thermoformer press forming station, the system featuring increased platen stability and also a decreased motor load in the midrange of the toggle motion.
Pairs of double toggle mechanisms have heretofore been known to be used to drive press platens operated by one or more motors driving a crank which drives two double toggle mechanisms. Each double toggle mechanism comprises one pair of links connected at one end to a platen and at their other ends are pivoted to one end of a second pair of links which are pivoted to the machine frame. A connector link connects the pivoted connections of the links together, and a crank driven drive link each connected to one end of a connector link operates each toggle mechanism.
The previous arrangements used resulted in an unstable platen motion which could tilt slightly particularly when under heavy load clue to unbalanced forces applied to the toggle mechanisms and twisting at the connections to the crank drive shaft, and pivotal connections with the various links as well as other components.
It is an object of the present invention to improve the crank drive and the various connections between the other components to create symmetrical loading and stable movement of the platens.
In conventional double toggle mechanisms used to drive platens in such presses, the maximum force exerted on the platens occur at full advance to carry out a forming process. Electric servo motors have been used to operate the double toggle mechanisms, which mechanisms develop a very high mechanical advantage when approaching full stroke to thereby generate the high forces necessary for carrying out the forming process. However, the maximum motor load typically occurs appropriately midrange in the toggle mechanism motion since the considerable weight of the platens and molds must be lifted without much benefit from the mechanical advantage afforded by the toggle mechanisms. This is because the toggle mechanisms only develop a modest mechanical advantage at that point in the toggle mechanism motion. A lower power motor could be used if the motor load were reduced at that point.
It is another object of the present invention to arrange the electric motor-crank drive to the toggle mechanism so as to reduce the peak motor load of the drive motor to allow a reduction in the size of the servo motor required to drive the toggle mechanisms.